The invention relates to a press roller with adjustable bending characteristics, especially for use in the paper industry, and comprising a hollow roller shell rotatable about a stationary support device including a yoke. The roller shell is adapted to cooperate with a counter roller to define a pressure nip which receives a web of paper. The axes of rotation of the two rollers and the pressure nip lie in a pressure plane.
A roller of this kind is known from DE-OS No. 30 03 395, which corresponds to U.S. Pat. No. 4,307,501. There, a hydraulic supporting device transmits supporting forces from a fixed yoke onto a rotatable roller shell. The supporting device comprises an annulus situated between the roller shell and the yoke. The annulus is divided by two axially extending seals into two semi-circular pressure chambers which are arranged symmetrically with respect to the plane of pressure. One pressure chamber faces the counter roller and may be supplied with a higher pressure than the other pressure chamber. The differential pressure between the two pressure chambers determines the course (or distribution) of the pressure in the pressure nip between the press roller and the counter roller. Altering the differential pressure alters the distribution of the line of nip pressure, corresponding to the natural bending lines of the press roller and the counter roller. A correcting device for localized alteration of the supporting forces comprises individual pistons positioned in the annulus between the yoke and roller shell, and preferably in the end areas of the press roller. In the inner area of the pistons, essentially only atmospheric pressure prevails. In this way, additional bending moments may be exerted on the roller shell. It is thereby possible to arbitrarily alter the bending line of the roller shell.
This known roller has some disadvantages, however. In contrast to older, known constructions, in which only the pressure chamber facing the counter roller is acted upon by a pressure medium, it is necessary to supply both pressure chambers with a pressure medium. A relatively high pump pressure is necessary, which implies high energy consumption. A further complication is that the aforementioned pistons cause additional friction and unequal heating of the shell over its breadth in the axial direction. Another disadvantage is that the pistons must be located in clearances in the yoke. These clearances reduce the stiffness and the firmess of the yoke.